Process for preparing 3,4,5,6-tetrahydrophthalic anhydrides or derivatives thereof

ABSTRACT

Δ 1  -THPA or a derivative thereof is prepared by isomerizing Δ 4  -THPA or a derivative thereof in the presence of (a) a palladium catalyst, and (b) an inorganic salt and/or a sulfur compound.

TECHNICAL FIELD

This invention relates to a process for preparing3,4,5,6-tetrahydrophthalic anhydrides or derivatives thereof.

BACKGROUND ART

It is known that 3,4,5,6-tetrahydrophthalic anhydrides (hereinafterabbreviated as "Δ¹ -THPA") or methyl-substituted derivatives thereof areprepared usually by isomerizing 1,2,3,6-tetrahydrophthalic anhydrides(hereinafter abbreviated as "Δ⁴ -THPA") or methyl-substitutedderivatives thereof. Various processes for the isomerization are known,but they are still unsatisfactory in yield and the purity of theproduct. For example, the process in which an inorganic strong acid,such as phosphoric acid, phosphorus pentoxide, sulfuric acid or thelike, is used as a catalyst has the drawback that the starting materialundergoes marked oxidation during reaction, affording Δ¹ -THPA in lowyields. Another conventional process in which palladium is used as acatalyst permits a disproportionation reaction in addition to theisomerization reaction, giving large amounts of phthalic anhydride andhexahydrophthalic anhydride as by-products to present difficulties inaffording the desired product with a high purity. When producing thedesired product with a high quality by these known processes, thereaction must be followed by distillation, recrystallization or likepurifying procedure, which results in an increase in the number of stepsas well as in cost and renders the process commercially unfavorable.Further if the yield is extremely low, it will be substantiallyimpossible to resort to purification.

We have found that Δ⁴ -THPA or a derivative thereof, when isomerized inthe presence of a palladium catalyst and a specific compound, gives Δ¹-THPA or a derivative thereof in a very high yield with a high purity.

An object of the invention is to provide a process for preparing Δ¹-THPA or derivatives thereof with a high quality almost free fromby-products, for example, due to disproportionation.

Another object of the invention is to provide a process for preparing Δ¹-THPA or derivatives thereof in high yields with an easy procedure ofpurification.

DISCLOSURE OF INVENTION

The present invention provides a process for preparing Δ¹ -THPA or aderivative thereof represented by the formula ##STR1## wherein R₁ and R₂are each hydrogen or methyl, characterized in that Δ⁴ -THPA or aderivative thereof represented by the formula ##STR2## where R₁ and R₂are as defined above is isomerized in the presence of (a) a palladiumcatalyst, and (b) an inorganic salt and/or a sulfur compound.

Examples of Δ⁴ -THPA or derivatives thereof useful as the startingmaterials to be isomerized according to the invention are Δ⁴ -THPA,3-methyl-Δ⁴ -THPA, 4-methyl-Δ⁴ -THPA, 3,4-dimethyl-Δ⁴ -THPA,3,5-dimethyl-Δ⁴ -THPA, 3,6-dimethyl-Δ⁴ -THPA and 4,5-dimethyl-Δ⁴ -THPA.

The palladium catalyst can be in the single form of metallic palladiumbut may preferably comprise a carrier for example of carbon, alumina,silica, asbestos or the like and about 0.1 to about 10% by weight,preferably about 1 to about 5% by weight, of palladium deposited on thecarrier.

The isomerization reaction of the invention is conducted using thepalladium catalyst conjointly with an inorganic salt and/or a sulfurcompound.

Examples of useful inorganic salts are halides, nitrates, phosphates,etc. of alkali metals or alkaline earth metals. Typical of such saltsare lithium chloride, potassium chloride, sodium chloride, magnesiumchloride, calcium chloride, lithium bromide, potassium bromide, sodiumbromide, potassium iodide, magnesium iodide, calcium iodide, lithiumnitrate, potassium nitrate, sodium nitrate, magnesium nitrate, potassiumphosphate, sodium phosphate, magnesium phosphate, etc. These inorganicsalts, which may be added directly to the reaction system, can be usedas deposited on a carrier, preferably on the same carrier as palladium.

The sulfur compounds to be used are sulfur per se, and organic orinorganic compounds containing sulfur in the molecule. These compoundsexhibit high selectivity.

Useful sulfur-containing organic compounds include various examples,typical of which are represented by the formula

    R.sup.1 --S.sub.x --R.sup.2

wherein R¹ is C₁₋₂₀ alkyl, C₁₋₂₀ hydroxycarbonylalkyl, C₁₋₂₀alkoxycarbonylalkyl, aryl or aralkyl, R² is C₁₋₂₀ alkyl, C₁₋₂₀hydroxycarbonylalkyl, C₁₋₂₀ alkoxycarbonylalkyl, aryl or aralkyl, and xis an integer of 1 to 3. More specific examples of such compounds aremethyl mercaptan, ethyl mercaptan, butyl mercaptan, lauryl mercaptan,dibutyl sulfide, dilauryl sulfide, p-tolyl mercaptan, benzyl mercaptan,dibenzyl sulfide, dibenzyl disulfide, dibenzyl trisulfide, thioglycolicacid, thiopropionic acid, diethyl thiodiacetate, dilaurylthiodipropionate, 4,4'-thiobis(3-methyl-6-t-butylphenol), etc. Alkalimetal salts of mercaptans, thioglycolic acid and thiopropionic acid arealso usable.

Other useful sulfur-containing organic compounds are represented by theformula

    C(CH.sub.2 R.sup.3).sub.4

wherein R³ is hydrogen, C₁₋₂ alkyl or OCO(CH₂)_(n) SR⁴ and at least oneof R³ should be OCO (CH₂)_(n) SR⁴ in which R⁴ is hydrogen or C₁₋₂₀alkyl, and n is an integer of 1 to 5. Examples of such compounds aretrimethylolpropane trithioglycolate, pentaerythritol tetrathioglycolate,pentaerythritol-tetrakis-(3-laurylthiopropionate), etc. Alkali metalsalts of these compounds are also usable.

Still other useful compounds include thiophene, 1,4-dithiodiene and likecyclic organic sulfur compounds, trialkyl(C₁₋₂₀) trithiophosphite,tetraalkyl(C₁₋₄)thiuram mono- or poly-sulfide, and p-toluenesulfonicacid or alkali metal salts thereof.

Useful sulfur-containing inorganic compounds are sulfides, sulfites,sulfates, thiosulfates, thiophosphates, thiocyanates, etc. of alkalimetals or alkaline earth metals, exemplary of which are potassiumsulfide, sodium sulfide, potassium sulfite, sodium sulfite, potassiumsulfate, sodium sulfate, magnesium sulfate, calcium sulfate, sodiumthiosulfate, sodium thiophosphate, sodium thiocyanate, etc.

Sulfur and these sulfur compounds may be added directly to the reactionsystem, or can be used as deposited on a carrier, preferably on the samecarrier as palladium, in an amount of about 0.1 to about 10% by weightbased on the carrier. Sulfur or the sulfur compound, depending on theconcentration thereof, could act on the catalyst as a poison to inhibitthe isomerization, to say nothing of disproportionation, so that thecompound must be used in the reaction system in a strictly controlledconcentration. Our research has revealed that the amount of sulfur or asulfur compound suitable for use in the reaction system is in the rangeof about 1 to about 200 ppm, calculated as sulfur and based on Δ⁴ -THPAor a derivative thereof used as the starting material. Larger amountswill inhibit the isomerization, whereas lesser amounts will entail poorselectivity.

For the reaction of this invention, it is preferable to use about 0.01to about 5 parts (by weight, the same as hereinafter) of palladium(calculated as pure metal) and about 0.01 to about 50 parts of theinorganic salt per 1000 parts of Δ⁴ -THPA or a derivative thereof usedas the starting material. The sulfur compound, if used, should be usedin the specified amount mentioned. According to this invention, eitherone of the organic salt and the sulfur compound is usable with thepalladium catalyst, or both of them are usable with the catalyst.

With this invention, the starting material, the catalyst, etc. areplaced into a reactor equipped with a stirrer, reflux condenser andnitrogen gas inlet and subjected to isomerization reaction in a nitrogengas atmosphere. The reaction is conducted usually at about 130° to about260° C., preferably at about 150° to about 200° C. The reaction time isusually about 4 to about 20 hours although not limited particularly.

The process of this invention affords the desired Δ¹ -THPA or derivativethereof in exceedingly high yield.

Separation of the catalyst from the reaction mixture by filtration ordecantation affords the desired product as a finished product. Whennecessary, the product can be further purified as by distillation.

The invention will be described below with reference to examples.

EXAMPLES 1 TO 3

Predetermined amounts of Δ⁴ -THPA serving as the starting material, acatalyst comprising palladium deposited on a carrier and an inorganicsalt are placed into a four-necked flask equipped with a stirrer and areflux condenser and then subjected to reaction in a nitrogen gasatmosphere to prepare Δ¹ -THPA. Table 1 shows the amounts, reactionconditions, results, etc.

The compounds obtained are identified by NMR, UV and IR absorptionspectra. The proportions of the compounds in the product are determinedby gas chromatography.

In the table, "HHPA" stands for hexahydrophthalic anhydride, "PA" forphthalic anhydride and "Δ³ -THPA" for 1,2,3,4-tetrahydrophthalicanhydride.

                  TABLE 1                                                         ______________________________________                                        Example       1         2        3                                            ______________________________________                                        Amount of .increment..sup.4 -THPA                                                           100       100       100                                         (%)                                                                           Catalyst carrier                                                                            Carbon    Alumina   Carbon                                      Amount of Pd  5         5         5                                           deposit (%)                                                                   Amount of catalyst                                                                          0.3       0.3       0.1                                         (g)                                                                           Inorganic salt                                                                              Sodium    Sodium    Potassium                                                 chloride  chloride  bromide                                     Amount of inorganic                                                                         0.2       0.1       0.2                                         salt (g)                                                                      Reaction temp.                                                                              170       170       180                                         (° C.)                                                                 Reaction time (h)                                                                           9         8         7                                           Yield (g)     97        96        96                                          Composition of                                                                product (%)                                                                   .increment..sup.1 -THPA                                                                     93.0      92.0      95.5                                        HHPA          5.0       5.5       3.5                                         PA            2.0       2.5       1.0                                         .increment..sup.3 -THPA                                                                     Trace     Trace     Trace                                       ______________________________________                                    

EXAMPLES 4 TO 6

Δ⁴ -THPA is isomerized in the same manner as in Example 1 except thatthe catalyst used comprises palladium and an inorganic salt deposited ona carrier. Table 2 shows the results.

                  TABLE 2                                                         ______________________________________                                        Example      4          5         6                                           ______________________________________                                        Amount of .increment..sup.4 -THPA                                                          100        100       100                                         (%)                                                                           Composition of                                                                catalyst                                                                      Carrier      Carbon     Carbon    Carbon                                      Amount of Pd 2          5         5                                           deposit (%)                                                                   Inorganic salt                                                                             Potassium  Sodium    Magnesium                                                chloride   chloride  chloride                                    Amount of salt                                                                             10         15        30                                          deposit (%)                                                                   Amount of catalyst                                                                         0.5        0.2       0.2                                         (g)                                                                           Reaction temp.                                                                             180        180       190                                         (° C.)                                                                 Reaction time (h)                                                                          6          7         8                                           Yield (g)    96         97        97                                          Composition of                                                                product                                                                       .increment..sup.1 -THPA                                                                    94.0       96.5      92.0                                        HHPA         4.5        2.5       6.0                                         PA           1.5        1.0       2.0                                         .increment..sup.3 -THPA                                                                    Trace      Trace     Trace                                       ______________________________________                                    

EXAMPLES 7 TO 11

Δ⁴ -THPA is isomerized in the same manner as in Example 1 except that asulfur compound is used in place of the inorganic salt. Table 3 showsthe results.

                  TABLE 3                                                         ______________________________________                                        Example   7         8        9     10    11                                   ______________________________________                                        Amount of 1000      1000     1000  1000  1000                                 .increment..sup.4 -THPA (%)                                                   Catalyst  Carbon    Carbon   Carbon                                                                              Carbon                                                                              Carbon                               carrier                                                                       Amount of Pd                                                                            5         5        5     5     5                                    deposit (%)                                                                   Amount of 2         2        2     2     2                                    catalyst (g)                                                                  Sulfur    Lauryl    Dibutyl  Sulfur                                                                              Sodium                                                                              Mag-                                 compound  mercaptan sulfide        sulfide                                                                             nesium                                                                        sulfate                              Amount of S                                                                             0.02      0.01     0.01  0.01  2                                    compound (g)                                                                  Reaction temp.                                                                          180       180      190   190   180                                  (° C.)                                                                 Reaction time                                                                           12        12       10    12    10                                   (h)                                                                           Yield (g) 980       985      980   980   975                                  Product com-                                                                  position (%)                                                                  .increment..sup.1 -THPA                                                                 95.0      98.5     97.5  96.0  93.5                                 HHPA      3.0       1.2      2.0   3.0   5.0                                  PA        1.5       Trace    0.5   1.0   1.5                                  .increment..sup.3 -THPA                                                                 0.5       Trace    Trace Trace Trace                                ______________________________________                                    

EXAMPLES 12 TO 16

Δ⁴ -THPA is isomerized in the same manner as in Example 1 except thatthe catalyst used comprises palladium and a sulfur compound deposited ona carrier. Table 4 shows the results.

                  TABLE 4                                                         ______________________________________                                        Example   12      13      14      15    16                                    ______________________________________                                        Amount of 1000    1000    1000    1000  1000                                  .increment..sup.4 -THPA (%)                                                   Catalyst                                                                      composition                                                                   Carrier   Carbon  Carbon  Alumina Carbon                                                                              Carbon                                Amount of 5       5       5       2     5                                     Pd (%)                                                                        Sulfur    Sulfur  Sulfur  Lauryl  Sulfur                                                                              Calcium                               compound                  mercaptan     sulfate                               Amount of 2       1       1       0.5   10                                    compd. (%)                                                                    Amount of 2       2       1       4     2                                     catalyst (g)                                                                  Reaction temp.                                                                          180     180     175     190   190                                   (° C.)                                                                 Reaction time                                                                           12      8       8       8     8                                     (h)                                                                           Yield (g) 986     988     980     983   980                                   Product com-                                                                  position (%)                                                                  .increment..sup.1 -THPA                                                                 98.4    97.0    95.0    96.0  94.0                                  HHPA      1.1     2.0     3.0     2.8   4.0                                   PA        0.3     0.6     1.5     0.9   2.0                                   .increment..sup.3 -THPA                                                                 0.2     0.4     0.5     0.3   Trace                                 ______________________________________                                    

EXAMPLES 17 TO 20

The procedure of Example 7 is repeated except that 3-methyl-Δ⁴ -THPA or4-methyl-Δ⁴ -THPA is used as the starting material. Table 5 shows theresults. The position of the methyl substituent in the starting materialremains unchanged in the product obtained.

                  TABLE 5                                                         ______________________________________                                        Example  17        18        19      20                                       ______________________________________                                        Starting 3-Methyl- 3-Methyl- 4-Methyl-                                                                             4-Methyl-                                material .increment..sup.4 -THPA                                                                 .increment..sup.4 -THPA                                                                 .increment..sup.4 -THPA                                                               .increment..sup.4 -THPA                  Amount of                                                                              1000      1000      1000    1000                                     material (g)                                                                  Catalyst Carbon    Carbon    Carbon  Carbon                                   carrier                                                                       Amount of Pd                                                                           5         5         5       5                                        deposit (%)                                                                   Amount of                                                                              2         2         2       2                                        catalyst (g)                                                                  Sulfur   Dibutyl   Sodium    Lauryl  Sulfur                                   compound sulfide   sulfide   mercaptan                                        Amount of S                                                                            0.011     0.01      0.01    0.01                                     compound (g)                                                                  Reaction 180       220       220     180                                      temp. (°C.)                                                            Reaction 12        6         6       12                                       time (h)                                                                      Yield (g)                                                                              985       980       980     980                                      Product com-                                                                  position (%)                                                                  3- or 4-                                                                      Methyl-  93.0      95.0      90.0    85.0                                     .increment..sup.1 -THPA                                                       Methyl-  4.0       3.0       5.0     7.0                                      HHPA                                                                          Others   3.0       2.0       5.0     8.0                                      ______________________________________                                    

EXAMPLES 21 TO 24

The procedure of Example 12 is repeated except that 3-methyl-Δ⁴ -THPA or4-methyl-Δ⁴ -THPA is used as the starting material. Table 6 shows theresults.

                  TABLE 6                                                         ______________________________________                                        Example  21        22        23      24                                       ______________________________________                                        Starting 3-Methyl- 3-Methyl- 4-Methyl-                                                                             4-Methyl-                                material .increment..sup.4 -THPA                                                                 .increment..sup.4 -THPA                                                                 .increment..sup.4 -THPA                                                               .increment..sup.4 -THPA                  Amount of                                                                              1000      1000      1000    1000                                     material (g)                                                                  Catalyst                                                                      composition                                                                   Carrier  Carbon    Carbon    Carbon  Carbon                                   Amount of                                                                              5         5         5       5                                        Pd (%)                                                                        Sulfur   Sulfur    Sodium    Sulfur  Sodium                                   compound           sulfide           sulfide                                  Amount of S                                                                            1         1         1       1                                        compd. (%)                                                                    Amount of                                                                              2         2         2       2                                        catalyst (g)                                                                  Reaction 200       210       200     210                                      temp. (°C.)                                                            Reaction 10        8         10      8                                        time (h)                                                                      Yield (g)                                                                              985       986       980     980                                      Product com-                                                                  position (%)                                                                  3- or 4-                                                                      Methyl-  93.0      92.0      89.0    87.0                                     .increment..sup.1 -THPA                                                       Methyl-  4.0       5.0       6.0     8.0                                      HHPA                                                                          Others   3.0       3.0       5.0     5.0                                      ______________________________________                                    

EXAMPLES 25 AND 26

The procedure of Example 1 is repeated except that a methyl-Δ⁴ -THPA isused as the starting material. The results are shown in Table 7.

                  TABLE 7                                                         ______________________________________                                        Example         25          26                                                ______________________________________                                        Starting material                                                                             3-Methyl-   4-Methyl-                                                         .increment..sup.4 -THPA                                                                   .increment..sup.4 -THPA                           Amount of material                                                                            1000        1000                                              (g)                                                                           Catalyst carrier                                                                              Carbon      Carbon                                            Amount of Pd                                                                  deposit (%)     5           5                                                 Amount of catalyst                                                                            2           2                                                 (g)                                                                           Inorganic salt  Sodium      Sodium                                                            chloride    chloride                                          Amount of inorganic                                                                           2           2                                                 salt (g)                                                                      Reaction temp.  180         180                                               (°C.)                                                                  Reaction time   8           8                                                 (h)                                                                           Yield (g)       960         950                                               Composition of                                                                product (%)                                                                   3- or 4-Methyl- 92.0        85.0                                              .increment..sup.1 -THPA                                                       Methyl-HHPA     4.0         6.0                                               Others          4.0         9.0                                               ______________________________________                                    

EXAMPLES 27 AND 28

The procedure of Example 4 is repeated except that a methyl-Δ⁴ -THPA isused as the starting material. The results are shown in Table 8.

                  TABLE 8                                                         ______________________________________                                        Example        27           28                                                ______________________________________                                        Starting material                                                                            3-Methyl-    4-Methyl-                                                        .increment..sup.4 -THPA                                                                    .increment..sup.4 -THPA                           Amount of material                                                                           1000         1000                                              (g)                                                                           Composition of                                                                catalyst                                                                      Carrier        Carbon       Carbon                                            Amount of Pd   5            5                                                 deposit (%)                                                                   Inorganic salt Sodium       Sodium                                                           chloride     chloride                                          Amount of salt 15           15                                                deposit (%)                                                                   Amount of catalyst                                                                           2            2                                                 (g)                                                                           Reaction temp. 180          180                                               (°C.)                                                                  Reaction time (h)                                                                            8            8                                                 Yield (g)      970          960                                               Composition of                                                                product (%)                                                                   3- or 4-Methyl-                                                                              94.0         88.0                                              .increment..sup.1 -THPA                                                       Methyl-HHPA    4.0          5.0                                               Others         2.0          7.0                                               ______________________________________                                    

EXAMPLES 29 AND 30

The procedure of Example 1 is repeated except that 3,6-dimethyl-Δ⁴ -THPAserving as the starting material, a catalyst comprising palladium asdeposited on a carrier, and an inorganic salt or a sulfur compound areused. The results are shown in Table 9.

                  TABLE 9                                                         ______________________________________                                        Example           29         30                                               ______________________________________                                        Amount of starting                                                                              1000       1000                                             material (g)                                                                  Catalyst carrier  Carbon     Carbon                                           Amount of Pd      5          5                                                deposit (%)                                                                   Amount of catalyst                                                                              2          2                                                (g)                                                                           Inorganic salt or Sodium     Dibutyl                                          sulfur compound   chloride   sulfide                                          Amount of salt or 2          0.01                                             S compound (g)                                                                Reaction temp. (°C.)                                                                     190        190                                              Reaction time (h) 12         10                                               Yield (g)         950        960                                              Composition of                                                                product (%)                                                                   3,6-dimethyl-     89.0       90.0                                             .increment..sup.1 -THPA                                                       Dimethyl-HHPA     7.0        5.0                                              Others            4.0        5.0                                              ______________________________________                                    

EXAMPLES 31 AND 32

The procedure of Example 1 is repeated except that 3,6-dimethyl-Δ⁴ -THPAserving as the starting material and a catalyst comprising palladium,and an inorganic salt or sulfur compound deposited on a carrier areused. Table 10 shows the results.

                  TABLE 10                                                        ______________________________________                                        Example         31          32                                                ______________________________________                                        Amount of starting                                                                            1000        1000                                              material (g)                                                                  Composition of                                                                catalyst                                                                      Carrier         Carbon      Carbon                                            Amount of Pd    5           5                                                 deposit (%)                                                                   Inorganic salt  Potassium   Lauryl                                            or sulfur compd.                                                                              chloride    mercaptan                                         Amount of salt  15          1                                                 or S compd. (%)                                                               Amount of catalyst                                                                            2           2                                                 (g)                                                                           Reaction temp. (°C.)                                                                   180         180                                               Reaction time (h)                                                                             12          12                                                Yield (g)       960         970                                               Composition of                                                                product (%)                                                                   3,6-dimethyl-   90.0        92.0                                              .increment..sup.1 -THPA                                                       Dimethyl-HHPA   6.0         4.0                                               Others          4.0         4.0                                               ______________________________________                                    

Industrial Applicability

The Δ¹ -THPA compounds and derivatives thereof prepared by the processof this invention are useful as materials for agricultural andhorticultural fungicides, herbicides, etc., as epoxy resin curing agentsand also as materials for polyester resins.

We claim:
 1. A process for preparing a 3,4,5,6-tetrahydrophthalicanhydride or a derivative thereof represented by the formula ##STR3##wherein R₁ and R₂ are each hydrogen or methyl, in high yields of highpurity comprising isomerizing a 1,2,3,6,-tetrahydrophthalic anhydride ora derivative thereof represented by the formula ##STR4## wherein R₁ andR₂ are as defined above in the presence of (a) a palladium catalyst, and(b) an inorganic salt and/or a sulfur compound.
 2. A process as definedin claim 1 wherein the inorganic salt is a halide, nitrate or phosphateof an alkali metal or alkaline earth metal.
 3. A process as defined inclaim 1 wherein the sulfur compound is sulfur, a sulfur-containingorganic compound or a sulfur-containing inorganic compound.
 4. A processas defined in claim 1 wherein the sulfur-containing organic compound isat least one of compounds represented by the formula

    R.sup.1 --S.sub.x --R.sup.2

wherein R¹ is C₁₋₂₀ alkyl, C₁₋₂₀ hydroxycarbonylalkyl, C₁₋₂₀alkoxycarbonylalkyl, aryl or aralkyl, R² is C₁₋₂₀ alkyl, C₁₋₂₀hydroxycarbonylalkyl, C₁₋₂₀ alkoxycarbonylalkyl, aryl or aralkyl, and xis an integer of 1 to 3; compounds represented by the formula

    C(CH.sub.2 R.sup.3).sub.4

wherein R³ is hydrogen, C₁₋₂ alkyl or OCO(CH₂)_(n) SR⁴ and at least oneof R³ is OCO(CH₂)_(n) SR⁴ in which R⁴ is hydrogen or C₁₋₂₀ alkyl, and nis an integer of 1 to 5; cyclic organic sulfur compounds includingthiophene and 1,4-dithiodiene trialkyl(C₁₋₂₀) trithiophosphite;tetraalkyl (C₁₋₄)thiuram mono- or poly-sulfide; and p-toluenesulfonicacid or alkali metal salts thereof.
 5. A process as defined in claim 1wherein the sulfur-containing inorganic compound is at least one ofsulfides, sulfites, sulfates, thiosulfates, thiophosphates andthiocyanates of alkali metals or alkaline earth metals.
 6. A process asdefined in claim 1 wherein the inorganic salt is used in an amount ofabout 0.01 to about 50 parts by weight per 1000 parts by weight of thestarting material.
 7. A process as defined in claim 1 wherein the sulfurcompound is used in an amount of about 1 to about 200 ppm calculated assulfur and based on the starting material.